1. Field of the Invention
This invention relates to a method and an apparatus for producing and desanding crude oil by separating at least a portion of the sand produced with the crude oil from a producing interval (zone) penetrated by a wellbore prior to pumping the crude oil to the surface.
2. Brief Description of the Prior Art
Many times in gravel pack completions or other completions wherein sand is produced with the oil, the oil and entrained sand flow into the wellbore. The upward velocity of the oil in the wellbore is relatively low and the sand may settle out and eventually restrict production by covering all or portions of the productive interval. The resultant necessity for workovers requires additional equipment to circulate out the sand and may also cause fluid losses and possible damage to the producing formation. To prevent the accumulation of sand in the producing zone, completions have been used where the oil is drawn directly from the producing interval into a tubing string through which it is pumped, at a velocity sufficient to entrain the sand, directly to the surface. The pump is frequently at a substantial distance above the bottom of the tubing string, particularly in high production wells where the liquid level in the wellbore is relatively high. In such completions, both the oil and the sand are pumped to the surface. The tubing is typically sized so that the flow rate through the tubing is sufficiently high to maintain the sand in suspension as the crude oil is drawn into the tubing and pumped to the surface. Liquid velocities of about 0.5 ft./sec. are generally considered sufficient to maintain the sand in suspension in the produced liquids, i.e. crude oil, water and mixtures thereof.
Such completions result in the removal of at least a substantial portion of the entrained sand from the well. While such completions are effective to remove sand from the well, the mixture of sand and crude oil is abrasive and pumping this mixture results in a relatively short pump life. When gas is produced with the sand and crude oil, the presence of the gas results in reduced pump efficiency so that not only is the pump life short but the pump efficiency is relatively low.
Accordingly, a method and apparatus for removing sand from a sand/crude oil mixture produced from a subterranean producing zone prior to pumping the crude oil to the surface, has been sought.